The objective of this research project is to improve our understanding of the molecular mechanism of genetic recombination. For this objective, two major approaches will be undertaken. First, at the enzyme level, the characterization of the recombination enzyme, recB- recC DNase (ATP-dependent DNase) will be continued, in order to understand the complicated enzyme reaction and its precise role in recombination in vivo. The DNase reaction will be analyzed with the recently isolated and purified subunit proteins (recB and recC proteins) of the enzyme. The mechanism and biological significance of the association process which leads to the formation of intact enzyme molecules from these subunits will also be subject to biochemical and genetic studies. Second, the genetic transformation system in E. coli will be further studied and specialized transformation systems in E. coli will be developed. Although the E. coli transformation system will be useful for a variety of studies, our primary original (and continued) purpose for developing and improving the system, especially the specialized transformation system, has been to apply it to studies on the mechanism of recombination. With such a system, molecular events of the recombination process will be studied with genetically as well as biophysically well defined DNA molecules. It will also provide a sensitive biological assay method for the various types of molecular intermediates formed in the recombination process.